1. Field of the Invention
The invention relates to a pump and a drive device thereof, and more particularly to a metering pump and a drive device thereof.
2. Description of the Related Art
Metering pumps are widely used nowadays, and most of them use one-way valves as switches. However, there are several problems with the conventional metering pump: firstly, the one-way valve can only be switched on or off as pressure applied thereon is greater than elastic recovery force thereof, which is inconvenient for microsampling or chemical dosing; secondly, the one-way often fails as impurities exist; thirdly, the one-way often fails due to pressure at a liquid-inlet hole and a liquid-outlet hole.
To overcome the above-mentioned problems, another metering pump is invented. The metering pump comprises a plunger, a plunger sleeve, a liquid-inlet hole, a liquid-outlet hole, and a pump body. The plunger sleeve is disposed in the pump body and rotates therein. The plunger reciprocally slides in the plunger sleeve. As the liquid-inlet hole or the liquid-outlet hole on the plunger sleeve reaches a corresponding position on the pump body, connection between a pump cavity and a liquid-inlet channel or a liquid-outlet channel is established. Since no one-way valve is used, measurement deviation caused thereby is prevented. However, since the plunger sleeve rotates in the pump body, requirements for sealing and fitting accuracy between the liquid-inlet hole or the liquid-outlet hole and the pump body are high, which makes production of the metering pump difficult. In addition, moving tracks of the liquid-inlet hole and the liquid-outlet hole in the pump body are circular, and sealing gap therebetween cannot be easily adjusted. Lastly, since the plunger cannot deliver all liquid in the plunger sleeve to the outside over a complete travel distance, metering deviation occurs due to residual liquid.